STOCK-BASED COMPENSATION - Summary of Incentive Stock Units (Details) - Incentive Stock Units (ISUs)	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Number of Shares
Unvested at beginning of period (in shares)	8,046,399
ISUs granted (in shares)	3,336,396
ISUs vested (in shares)	(4,396,417)
ISUs forfeited (in shares)	(227,445)
Unvested at end of period (in shares)	6,758,933
Vested and unreleased (in shares)	183,569
Outstanding at end of period (in shares)	6,942,502
Weighted Average Grant Date Fair Value
Unvested at beginning of period (in USD per share) | $ / shares	$ 3.41
ISUs granted (in USD per share) | $ / shares	4.82
ISUs vested (in USD per share) | $ / shares	5.20
ISUs forfeited (in USD per share) | $ / shares	3.45
Unvested at end of period (in USD per share) | $ / shares	$ 3.79